by November 5, 2002 0 comments



USB On-the-Go (OTG) is a supplement to the new USB 2.0 specification and is designed to allow USB devices to talk to each other directly. This is in contrast with the ‘traditional’ USB that needs a PC in order to allow them to communicate amongst themselves. For example, currently you cannot have your USB camera print directly to your USB printer–it takes a PC to broker a deal between them. 

Traditional USB technology defines two major roles–that of a host and a peripheral. A host is a device which has USB host controller functionality built into it. It stores all the device drivers and control information which is necessary to talk to other USB devices. This information allows a host to talk to other USB devices. Your PC, which is fitted with a USB controller chip, is the most common example of a host. Any USB device without the controller is a peripheral. Printers and cameras are peripherals.Peripherals need to be connected to a host.

But USB OTG is set to change all that. It adds ‘limited host’ capability to USB devices themselves, which means that they can now connect and exchange data with other USB devices directly, bypassing the PC. This is done by adding a special chip in these devices that allows them to act either as a host or as a regular peripheral. For example, when connected to a PC the device would act as a peripheral, but when connected with another peripheral, it automatically takes over as the host. If both the devices are capable of playing the host, they agree to let one act as the host, while the other becomes the peripheral. All this is done automatically without user knowledge or intervention.

Standard Max
Speed (Mbps)
Max
Cable Length (meters)
Max
number of 
connected devices
Require
Computer (Yes/No)
USB 1.1 12 5 127 Yes
FireWireIEEE 1394a 400 4.5 64 No
USB 2.0 480 5 127 No
FireWire IEEE 1394b 1600 4.5 64 No

Those familiar with technology will be quick to point out that IEEE 1394 or FireWire, as it is better known has supported this for quite some time now. So why all this fuss now? FireWire, for all its technical superiority hasn’t quite caught on as well as USB. Call it marketing or anything else but, truth be told, no other comparable technology has quite captured the imagination of the public as USB has. OTG and USB 2.0 have furthered the case of USB by making the connectors smaller as well as by lowering power requirements considerably. Add to that the fact, that USB has always been cheaper to implement than FireWire, and it becomes easier to understand why OTG is exciting news. New devices with OTG capability can also connect to older USB devices as they can act as the host to the older devices. 

This initiative has the backing of the who’s who of the computer world including Compaq, Hewlett-Packard, Intel, Lucent, Microsoft and NEC. TransDimension and Philips Electronics are two big name manufacturers who sell the chips necessary to build USB On-the-Go devices. These companies expect to roll out cameras that could print directly to printers by the end of this year. Also on the anvil are cell phones that could exchange data with your PDA and/ or download music from your MP3 player. More information is available from
www.usb.org/developers/onthego/.

Kunal Dua

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